Methods of forming conductive material silicides by reaction of metal with silicon

ABSTRACT

A method of forming a conductive metal silicide by reaction of metal with silicon is described. A method includes providing a semiconductor substrate with an exposed elemental silicon-containing surface. At least one of a nitride, boride, carbide, or oxide-comprising layer is atomic layer deposited onto the exposed elemental silicon-containing surface to a thickness no greater than 15 Angstroms. This ALD-deposited layer is exposed to plasma and a conductive reaction layer including at least one of an elemental metal or metal-rich silicide is deposited onto the plasma-exposed layer. Metal of the conductive reaction layer is reacted with elemental silicon of the substrate effective to form a conductive metal silicide-comprising contact region electrically connecting the conductive reaction layer with the substrate. Other aspects and implementations are contemplated.

TECHNICAL FIELD

This invention relates to methods of forming conductive metal silicidesby reaction of metal with silicon.

BACKGROUND OF THE INVENTION

Integrated circuits typically use various combinations of insulativematerials, conductive materials, and semiconductive materials (includingconductively doped semiconductive material). One type of conductivematerial which is utilized is elemental metals. In the context of thisdocument, an “elemental metal” is defined to mean any one or more metalelement(s) in element form, including any alloy of two or more metalelements. In many instances, it is desired to form a metal intoelectrical connection with a crystalline silicon substrate, for exampleconductively doped crystalline silicon. However, the physical contact ofan elemental metal with a crystalline silicon substrate inherentlycreates undesired excessive electrical resistance between the twomaterials.

One common way of reducing this resistance is to form an interfacingsilicide region at the junction or interface of the metal with thesilicon. Thereby, a silicon-silicide-metal interfacing electricalconnection is formed. One manner of forming the silicide is merely byheating the substrate with the two contacting layers to a suitabletemperature for a sufficient period of time, typically in an inertatmosphere, to cause a reaction of metal and silicon to form the metalsilicide. Alternately or in addition thereto, the deposition conditionsfor the metal material deposited over the silicon can be effectivelyhigh to impart a reaction of the depositing metal with the underlyingsilicon in situ during deposition. Regardless, the silicide which formsresults from reaction of the metal with the underlying siliconsubstrate. The reaction is typically self-limiting such that furtherprocessing or exposure to temperature at some point stops resulting insilicide formation.

Integrated circuitry fabrication continues to strive to make ever denserand smaller electronic devices of the circuitry. One place wheresilicide contact structures are utilized is in the electrical connectionof source/drain diffusion regions of field effect transistors withoverlying conductive metal lines. As the device components get smallerand denser, it is highly desirable to precisely control the amount ofsilicide which is formed in such contacts, as well as in other deviceswhere silicide interfaces between metal and silicon are desired to beformed. For example in some instances in present-generation processing,it is desirable to fabricate the silicide regions over the substrates tohave thicknesses of from 50 Angstroms to 100 Angstroms. Further, it isexpected that the thickness of silicide regions in later-generationprocessing will fall below 50 Angstroms. Regardless, the variation inthickness of silicide regions formed over a substrate using typicalprior art processing has been found to be anywhere from 20 Angstroms to25 Angstroms across the substrate. This variability is undesirable andconstitutes a 20% to 25% thickness variation for desired 100 Angstromsthick silicide regions, and a 40% to 50% variation in thickness fordesired 50 Angstroms thick silicide regions. It would be desirable todevelop methods which enable tighter thickness control of silicideregions which are formed across a substrate, and particularly where thesilicide regions being formed have thicknesses that are no greater than100 Angstroms where the above problem particularly manifests.

While the invention was motivated in addressing the above describedissues, it is in no way so limited. The invention is only limited by theaccompanying claims as literally worded, without interpretative or otherlimiting reference to the specification, and in accordance with thedoctrine of equivalents.

SUMMARY

The invention includes methods of forming conductive metal silicides byreaction of metal with silicon. In one implementation, such a methodincludes providing a semiconductor substrate comprising an exposedelemental silicon containing surface. At least one of a nitride, boride,carbide, or oxide comprising layer is atomic layer deposited onto theexposed elemental silicon containing surface to a thickness no greaterthan 15 Angstroms. Such layer is exposed to plasma and a conductivereaction layer comprising at least one of an elemental metal or metalrich silicide is deposited onto the plasma exposed layer. Metal of theconductive reaction layer is reacted with elemental silicon of thesubstrate effective to form a conductive metal silicide comprisingcontact region electrically connecting the conductive reaction layerwith the substrate.

Other aspects and implementations are contemplated.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic sectional view of a semiconductor waferfragment in process in accordance with an aspect of the invention.

FIG. 2 is a view of the FIG. 1 fragment at a processing step subsequentto that shown by FIG. 1.

FIG. 3 is a view of the FIG. 1 fragment at a processing step subsequentto that shown by FIG. 2.

FIG. 4 is view of the FIG. 1 fragment at a processing step subsequent tothat shown by FIG. 2.

FIG. 5 is a view of the FIG. 1 fragment at a processing step subsequentto that shown by FIG. 2.

FIG. 6 is a diagrammatic sectional view of an alternate embodimentsemiconductor wafer fragment in process in accordance with an aspect ofthe invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

Exemplary preferred methods of forming a conductive metal silicide byreaction of metal with silicon are described with reference to FIGS.1-6. Referring initially to FIG. 1, a substrate fragment is indicatedgenerally with reference numeral 10, and comprises a semiconductorsubstrate 12. In the context of this document, the term “semiconductorsubstrate” or “semiconductive substrate” is defined to mean anyconstruction comprising semiconductive material, including, but notlimited to, bulk semiconductive materials such as a semiconductive wafer(either alone or in assemblies comprising other materials thereon), andsemiconductive material layers (either alone or in assemblies comprisingother materials). The term “substrate” refers to any supportingstructure, including, but not limited to, the semiconductive substratesdescribed above. Accordingly, semiconductor substrate 12 might comprisevarious structures and/or composites and/or mixtures of insulative,conductive and semiconductive materials. Regardless in the context ofthe invention, semiconductor substrate 12 comprises some exposedelemental silicon containing surface 14. Such might be a substantiallyglobal surface across the entirety of the substrate being processed, orone or more isolated regions of exposed elemental silicon. For example,and by way of example only, an exposed silicon surface might constitutethe outer surface of a conductive diffusion region formed ofconductively doped monocrystalline or polycrystalline silicon exposedthrough a contact opening formed in an insulative material layer orlayers. Regardless in one aspect, exposed elemental silicon containingsurface 14 comprises monocrystalline silicon (including epitaxiallygrown silicon) and/or polycrystalline silicon. Exposed elemental siliconcontaining surface also or alternately might comprise silicon from asilicon-rich silicon compound.

Referring to FIG. 2, a layer 16 comprising at least one of a nitride,boride, carbide or oxide is atomic layer deposited onto exposedelemental silicon containing surface 14 to a thickness no greater than15 Angstroms. Accordingly, layer 16 might comprise any one orcombination of nitrides, borides, carbides or oxides. Atomic layerdepositing (ALD) typically involves formation of successive atomiclayers on a substrate. Such layers may comprise, for example, epitaxial,polycrystalline, and/or amorphous material. Described in summary, ALDincludes exposing an initial substrate to a first chemical species toaccomplish chemisorbtion of the species onto the substrate.Theoretically, the chemisorbtion forms a monolayer that is uniformly oneatom or molecule thick on the entire exposed initial substrate. In otherwords, a saturated monolayer is preferably formed. Practically,chemisorbtion might not occur on all portions or completely over thedesired substrate surfaces. Nevertheless, such an imperfect monolayer isstill considered a monolayer. In many applications, merely asubstantially saturated monolayer may be suitable. A substantiallysaturated monolayer is one that will still yield a deposited layerexhibiting the quality and/or properties desired for such layer.

The first species is purged from over the substrate and a secondchemical species is provided to chemisorb onto the first monolayer ofthe first species. The second species is then purged and the steps arerepeated with exposure of the second species monolayer to the firstspecies. In some cases, the two monolayers may be of the same species.Also, a third species or more may be successively chemisorbed and purgedjust as described for the first and second species. Further, one or moreof the first, second and third species can be mixed with inert gas tospeed up pressure saturation within a reaction chamber.

Purging may involve a variety of techniques including, but not limitedto, contacting the substrate and/or monolayer with a carrier gas and/orlowering pressure to below the deposition pressure to reduce theconcentration of a species contacting the substrate and/or chemisorbedspecies. Examples of carrier gases include N₂, Ar, He, Ne, Kr, Xe, etc.Purging may instead include contacting the substrate and/or monolayerwith any substance that allows chemisorption byproducts to desorb andreduces the concentration of a species preparatory to introducinganother species. A suitable amount of purging can be determinedexperimentally as known to those skilled in the art. Purging time may besuccessively reduced to a purge time that yields an increase in filmgrowth rate. The increase in film growth rate might be an indication ofa change to a non-ALD process regime and may be used to establish apurge time limit.

ALD is often described as a self-limiting process in that a finitenumber of sites exist on a substrate to which the first species may formchemical bonds. The second species might only bond to the first speciesand thus may also be self-limiting. Once all of the finite number ofsites on a substrate are bonded with a first species, the first specieswill often not bond to other of the first species already bonded withthe substrate. However, process conditions can be varied in ALD topromote such bonding and render ALD not self-limiting. Accordingly, ALDmay also encompass a species forming other than one monolayer at a timeby stacking of a species, forming a layer more than one atom or moleculethick. Further, local chemical reactions can occur during ALD (forinstance, an incoming reactant molecule can displace a molecule from anexisting surface rather than forming a monolayer over the surface). Tothe extent that such chemical reactions occur, they are generallyconfined within the uppermost monolayer of a surface.

Traditional ALD can occur within frequently-used ranges of temperatureand pressure and according to established purging criteria to achievethe desired formation of an overall ALD layer one monolayer at a time.Even so, ALD conditions can vary greatly depending on the particularprecursors, layer composition, deposition equipment, and other factorsaccording to criteria known by those skilled in the art. Maintaining thetraditional conditions of temperature, pressure, and purging minimizesunwanted reactions that may impact monolayer formation and quality ofthe resulting overall ALD layer. Accordingly, operating outside thetraditional temperature and pressure ranges may risk formation ofdefective monolayers.

With respect to layer 16, exemplary preferred nitrides include tantalumnitride, titanium nitride, tungsten nitride, boron nitride, aluminumnitride, hafnium nitride, and mixtures thereof. Preferably where anynitride is present, such nitride is void of silicon nitride due to itsexcessive resistivity. Exemplary preferred borides include tungstenboride, titanium boride, and mixtures thereof. Exemplary preferredcarbides include tantalum carbide, titanium carbide, silicon carbide,and mixtures thereof. Exemplary preferred oxides include rhodium oxide,ruthenium oxide, iridium oxide, and mixtures thereof. Where oxide ispresent, such is preferably void of SiO₂ due to its excessiveresistance. While the disclosed invention does not preclude presence oruse of silicon nitride or silicon dioxide, such are not preferred.Further preferably, exposed elemental silicon containing surface 14 issubjected to an HF dip prior to atomic layer depositing of layer 16thereover.

ALD layer 16 preferably has a thickness which is no less than 5Angstroms, with a more preferred thickness range being from 5 Angstromsto 10 Angstroms.

In one implementation, layer 16 as-deposited to a thickness no greaterthan 15 Angstroms has a resistance greater than 1000 microohms-cm.

In one exemplary preferred reduction-to-practice example, layer 16comprises tantalum nitride, for example atomic layer deposited fromprecursors comprising pentakis-dimethylamido-tantalum (PDMAT) andammonia. For example, and by way of example only, atomic layerdeposition conditions include a substrate temperature of from 125° C. to400° C., PDMAT carrier gas flow (Ar) in the range of 100 sccm to 175sccm, and NH₃ flow in the range of 1000 sccm to 1750 sccm. Exemplarypreferred cycle sequences include 75 milliseconds to 2000 millisecondsof PDMAT pulse length, 250 milliseconds to 2250 milliseconds of Ar purgeafter each PDMAT pulse, 125 milliseconds to 2500 milliseconds of NH₃pulse length, and 500 milliseconds to 2000 milliseconds Ar purge aftereach NH₃ pulse. A specific example, and by way of example only, is 500millisecond PDMAT pulses, 500 millisecond Ar purges, 1000 millisecondNH₃ pulses, and 500 millisecond Ar purges. Precursor carrier and NH₃flows were 100 sccm and 1000 sccm, respectively. Growth rate ofapproximately 0.7 Angstroms per cycle was achieved, indicating eachcycle was not resulting in complete saturation. A more preferredtemperature range is from 175° C. to 300° C., with 275° C. being aspecific preferred example.

Referring to FIG. 3, ALD layer 16 has been exposed to plasma and aconductive reaction layer 18 comprising at least one of an elementalmetal or metal rich silicide has been deposited onto plasma exposedlayer 16. Metal of conductive reaction layer 18 is reacted withelemental silicon of substrate 12 effective to form a conductive metalsilicide comprising contact region 20 which electrically connectsconductive reaction layer 18 with substrate 12. Conductive metalsilicide comprising contact region 20 preferably has a thickness from 5Angstroms to 100 Angstroms. FIG. 3 depicts an upper un-reacted portion22 of conductive reaction layer 18, whereby a lower portion of layer 18has reacted to form silicide with silicon of substrate 12. In onepreferred example, outer portion 22 of conductive reaction layer 18 atleast predominately comprises elemental metal, and in another exampleconsists essentially of elemental metal. In one exemplary embodiment,outer portion 22 of conductive reaction layer 18 at least predominatelycomprises metal rich silicide, and in another example consistsessentially of metal rich silicide. By way of example only, exemplaryelemental metals include titanium, nickel, ruthenium, cobalt, tungsten,iridium, molybdenum, and mixtures thereof. Exemplary metal richsilicides include metal silicides of these exemplary metals, includingmixtures thereof. In one embodiment, the at least one of a nitride,boride, carbide, or oxide of layer 16 of FIG. 2 is of a metal which isdifferent from the metal of the conductive reaction layer. In oneexemplary embodiment, the at least one of the nitride, boride, carbide,or oxide of layer 16 of FIG. 2 is of a metal which is the same as themetal of the conductive reaction layer.

One exemplary preferred and reduction-to-practice material forconductive reaction layer 18 comprises at least one of titanium andtitanium rich titanium silicide. Further by way of example only,titanium and titanium rich titanium silicides can be deposited utilizinghalides, such as TiCl₄. An exemplary preferred technique for depositingelemental titanium utilizes a capacitively coupled, single waferprocessor, for example a Centura™ reactor available from AppliedMaterials of Santa Clara, Calif. Exemplary substrate temperatureconditions during deposit of either a titanium or titanium rich metalsilicide layer include from 550° C. to 700° C. An exemplary preferredpressure range is from 1 Torr to 10 Torr, with an exemplary RF appliedpower being from 50 Watts to 500 Watts. An exemplary flow rate of theTiCl₄ is from 50 mg/min to 500 mg/min, with an exemplary additional gasflows of Ar and H₂ each being from 50 sccm to 500 sccm. If a titaniumrich titanium silicide is to be deposited, a suitable silane could alsobe flowed and/or pulsed to the deposition reactor at volumetric flowrates sufficiently spaced or suitably low to result in excess elementaltitanium in the titanium silicide layer being formed. Conductivereaction layer 18 might be of the same, greater or lesser thickness asthat of crystalline form layer 16, with greater thickness beingpreferred.

The above stated exposing of the ALD layer to plasma, the depositing ofa conductive reaction layer, and the reacting to form a conductive metalsilicide comprising contact region can occur separately or in variouscombinations. For example where a conductive reaction layer depositingis by a plasma deposition, such act of depositing with plasma canconstitute some or all of the ALD layer exposing to plasma. Accordinglyin such example, at least some of such ALD layer exposing to plasmaoccurs during the depositing of the conductive reaction layer. If thereis no plasma exposure of the ALD layer prior to a plasma deposition ofthe conductive layer, then the exposing would only occur during a plasmadeposition of the conductive reaction layer.

FIG. 4 diagrammatically depicts by the downwardly directed arrows ALDlayer 16 being exposed to plasma prior to and separate of the depositingof conductive reaction layer 18 as depicted by FIG. 3. As stated above,some plasma exposure of layer 16 is contemplated in accordance with theinvention. Such plasma exposure might all occur during the deposition ofthe conductive reaction layer, all of such exposing prior to andseparate of the deposition of the conductive reaction layer, or bothbefore and during deposition of the conductive reaction layer.

Further regarding reacting of metal of the conductive reaction layerwith elemental silicon of the substrate to form a conductive metalsilicide comprising contact region, such reacting might occur during theconductive reaction layer depositing, after the depositing, or bothduring and after the depositing. By way of example only, FIG. 5 depictsa conductive reaction layer 18 deposited over ALD layer 16 in a mannerwherein negligible if any reaction to form a conductive metal silicidecomprising contact region occurs. Such might result if deposition oflayer 18 were conducted at suitably low temperatures to precludeappreciable reaction of metal of layer 18 with silicon of substrate 12,with or without plasma. If so and regardless, a silicidation reactionbetween metal of layer 18 and silicon of substrate 12 could be achievedby exposure of the substrate to a suitable temperature, for example from400° C. to 700° C. for an exemplary time period of from 30 seconds to 5minutes to, for example, produce the structure of FIG. 3. Regardless, itis possible that the combination of the exposing, depositing, andreacting might be effective to substantially break up and/or diffuselayer 16 relative to one or both of conductive reaction layer 18 orregion 20 such that layer 16 may no longer be distinguishable or havethe same boundaries as initially deposited.

Processing as described in the above exemplary preferred embodimentsproduces certain unexpected advantages and results. However, suchadvantages or results do not constitute part of the invention unlessliterally appearing in a particular claim under analysis. In onepreferred implementation, the exposing of the ALD layer to plasma andreacting to form the conductive metal silicide comprising contact regionis effective to reduce resistance of the ALD layer to have an intrinsicresistance less than 1000 microohms-cm, and more preferably to have anintrinsic resistance less than 800 microohms-cm. For example, depositionof an elemental titanium layer by PECVD as described above wasdiscovered to reduce intrinsic resistivity of an ALD tantalum nitridefilm of from 5 Angstroms to 10 Angstroms in thickness to about 700microohms-cm. This was unexpected as the as-deposited film had intrinsicresistance well in excess of 1000 microohms-cm. The mechanism for suchadvantageous results is not fully understood. Without being limited toany theory of invention, one possibility is tunneling or diffusion ofthe formed silicide material through the ALD layer of thickness nogreater than 15 Angstroms. An alternate or additional theory is that theplasma attack or exposure onto the ALD layer is favorably reducingresistivity of such layer. An alternate or additional theory is that theexposure to plasma, the depositing of the conductive reaction layer, andthe reacting to form metal silicide is resulting in layer 16 not beingcontinuous, thereby enhancing conductivity (reducing resistivity).Further and regardless, some or much of layer 16 from one or more ofsuch acts might be diffusing into and relative to silicide region 20being formed. Regardless, in one aspect of the invention resistance isreduced to a value below 1000 microohms-cm, and more preferably to avalue below 800 microohms-cm.

Another advantageous result in one implementation is that the exposing,depositing and reacting result in better control (less variation) in thethickness of the metal silicide formed by the reaction. Accordingly inone implementation, the exposing, depositing and reacting are effectiveto form all conductive metal silicide formed over the substrate by thereacting to have no more than 10% thickness variation as determined asthe percentage of the thickness portion of the conductive metal silicideformed by the reacting. In another preferred implementation, suchthickness variation is from 1% to 3%, and in another preferredembodiment to have no more than 1% of such thickness variation. In oneexemplary reduction-to-practice example, a thickest deposited portion ofa metal silicide formed by the reacting was to 50 Angstroms, with thethickness variation across the substrate never exceeding 0.5 Angstrom ofthe metal silicide formed by the reacting.

By way of example only, FIG. 6 depicts an alternate exemplary embodimentsubstrate fragment 10 a. Like numerals form the first describedembodiments are utilized where appropriate, with differences beingindicated with the suffix “a” or with different numerals. FIG. 6 depictsinsulative material 30, for example comprising borophosphosilicate glassand undoped SiO₂, having been deposited over substrate 12. A contactopening 32 has been formed therethrough effective to expose someelemental silicon containing surface of substrate 12. Layer 16 b,comprising at least one of a nitride, boride, carbide, or oxidecomprising layer having a thickness no greater than 15 Angstroms, hasbeen deposited. Processing has occurred in accordance with the broadestaspects above, including any of the various preferred attributes,effective to form conductive metal silicide comprising contact region 20a which electrically connects conductive reaction layer 18 a withsubstrate 12. Further processing could occur, of course, including theforming of additional layers or the removing of the depicted layerswithout departing form the spirit and scope of the invention.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood however, that the invention is not limited to thespecific features shown and described, since the means herein disclosedcomprise preferred forms of putting the invention into effect. Theinvention is, therefore, claimed in any of its forms or modificationswithin the proper scope of the appended claims appropriately interpretedin accordance with the doctrine of equivalents.

1. A method of forming a conductive metal silicide by reaction of metalwith silicon, comprising: providing a semiconductor substrate comprisingan exposed elemental silicon-containing surface; atomic layer depositingat least one of a nitride, boride, carbide, or oxide-comprising layeronto the exposed elemental silicon-containing surface to a thickness nogreater than 15 Angstroms; exposing the layer of thickness no greaterthan 15 Angstroms to plasma and depositing a conductive reaction layercomprising at least one of a first elemental metal or metal-richsilicide onto the plasma-exposed layer; and reacting said first metal ormetal-rich silicide of the conductive reaction layer with elementalsilicon of the substrate effective to form a conductive metalsilicide-comprising contact region electrically connecting theconductive reaction layer with the substrate.
 2. The method of claim 1,wherein the atomic layer depositing is of a nitride-comprising layer. 3.The method of claim 2, wherein the nitride comprising layer comprises anitride selected from the group consisting of tantalum nitride, titaniumnitride, tungsten nitride, boron nitride, aluminum nitride, hafniumnitride, and mixtures thereof.
 4. The method of claim 2, wherein thenitride comprising layer is void of Si₃N₄.
 5. The method of claim 1,wherein the atomic layer depositing is of a boride comprising layer. 6.The method of claim 5, wherein the boride comprising layer comprises aboride selected from the group consisting of tungsten boride, titaniumboride, and mixtures thereof.
 7. The method of claim 1, wherein theatomic layer depositing is of a carbide-comprising layer.
 8. The methodof claim 7, wherein the carbide-comprising layer comprises a carbideselected from the group consisting of tantalum carbide, titaniumcarbide, silicon carbide, and mixtures thereof.
 9. The method of claim1, wherein the atomic layer depositing is of an oxide-comprising layer.10. The method of claim 9, wherein the oxide-comprising layer comprisesan oxide selected from the group consisting of rhodium oxide, rutheniumoxide, iridium oxide, and mixtures thereof.
 11. The method of claim 9,wherein the oxide-comprising layer is void of SiO₂.
 12. The method ofclaim 1, wherein the at least one of a nitride, boride, carbide, oroxide is of a second metal which is different from said first metal ofthe conductive reaction layer.
 13. The method of claim 1, wherein the atleast one of a nitride, boride, carbide, or oxide is of a second metalwhich is the same as said first metal of the conductive reaction layer.14. The method of claim 1, wherein the layer of thickness no greaterthan 15 Angstroms is of a thickness no less than 5 Angstroms.
 15. Themethod of claim 1, wherein the layer of thickness no greater than 15Angstroms is of a thickness from 5 Angstroms to 10 Angstroms.
 16. Themethod of claim 1, wherein the exposed elemental silicon-containingsurface comprises polycrystalline silicon.
 17. The method of claim 1,wherein the exposed elemental silicon-containing surface comprisesmonocrystalline silicon.
 18. The method of claim 17, wherein themonocrystalline silicon comprises epitaxially-grown silicon.
 19. Themethod of claim 1, wherein the exposing occurs during the depositing.20. The method of claim 1, wherein the exposing only occurs during thedepositing.
 21. The method of claim 1, wherein at least some of theexposing occurs prior to and separate from the depositing.
 22. Themethod of claim 21, wherein all of the exposing occurs prior to andseparate from the depositing.
 23. The method of claim 1, wherein theconductive reaction layer has an outer portion that at leastpredominately comprises said first elemental metal.
 24. The method ofclaim 23, wherein the conductive reaction layer outer portion consistsessentially of said first elemental metal.
 25. The method of claim 1,wherein the conductive reaction layer has an outer portion that at leastpredominately comprises said metal-rich silicide.
 26. The method ofclaim 25, wherein the conductive reaction layer outer portion consistsessentially of said metal-rich silicide.
 27. The method of claim 1,wherein the reacting occurs during the depositing.
 28. The method ofclaim 1, wherein the reacting occurs after the depositing.
 29. Themethod of claim 28, wherein the reacting does not occur during thedepositing.
 30. The method of claim 1, wherein the exposing and thereacting occur during the depositing.
 31. The method of claim 1 whereinthe deposited layer of thickness no greater than 15 Angstroms has anas-deposited resistance greater than 1000 microohms-cm, the exposing andreacting being effective to reduce resistance of the deposited layer ofthickness no greater than 15 Angstroms to less than 1000 microohms-cm.32. The method of claim 31, wherein the exposing and reacting areeffective to reduce resistance of the deposited layer of thickness nogreater than 15 Angstroms to less than 800 microohms-cm.
 33. The methodof claim 31, wherein: the layer of thickness no greater than 15Angstroms is of a thickness from 5 Angstroms to 10 Angstroms; theexposing occurs during the depositing; and the reacting occurs duringthe depositing.
 34. The method of claim 1, wherein the layer ofthickness no greater than 15 Angstroms comprises tantalum nitride. 35.The method of claim 34, wherein the conductive reaction layer comprisesat least one of titanium and titanium-rich titanium silicide.
 36. Themethod of claim 34, wherein the tantalum nitride is atomic layerdeposited from precursors comprising pentakis-dimethylamido-tantalum andammonia.
 37. The method of claim 34, wherein the layer of thickness nogreater than 15 Angstroms is of a thickness from 5 Angstroms to 10Angstroms.
 38. The method of claim 34 wherein the conductive reactionlayer has an outer portion that at least predominately comprises saidfirst elemental metal.
 39. The method of claim 34, wherein theconductive reaction layer has an outer portion that at leastpredominately comprises said metal-rich silicide.
 40. The method ofclaim 1, wherein the conductive metal silicide-comprising contact regionhas a thickness from 5 Angstroms to 100 Angstroms.
 41. The method ofclaim 1, wherein the exposing, depositing and reacting are effective toform all conductive metal silicide formed over the substrate by thereacting to have no more than 10% thickness variation as determined of athickest portion of said conductive metal silicide formed by thereacting.
 42. The method of claim 1 wherein the exposing, depositing andreacting are effective to form all conductive metal silicide formed overthe substrate by the reacting to have no more than 1% thicknessvariation as determined of a thickest portion of said conductive metalsilicide formed by the reacting.
 43. The method of claim 1 wherein theexposing, depositing and reacting are effective to form all conductivemetal silicide formed over the substrate by the reacting to have from 1%to 3% thickness variation as determined of a thickest portion of saidconductive metal silicide formed by the reacting.
 44. The method ofclaim 1, wherein the conductive reaction layer is of a thickness whichis greater than that of the layer of thickness no greater than 15Angstroms.
 45. The method of claim 1, wherein the exposed elementalsilicon-containing surface is received within a contact opening formedwithin an insulative layer.
 46. A method of forming a conductive metalsilicide by reaction of metal with silicon, comprising: providing asemiconductor substrate comprising an exposed elemental siliconcontaining surface; atomic layer depositing a tantalum nitridecomprising layer onto the exposed elemental silicon containing surfaceto a thickness no greater than 15 Angstroms, the deposited tantalumnitride-comprising layer having a resistance greater than 1000microohms-cm; exposing the tantalum nitride-comprising layer ofthickness no greater than 15 Angstroms to plasma and depositing aconductive reaction layer comprising at least one of an elemental metalor metal-rich silicide onto the plasma-exposed layer; and reacting saidmetal or metal-rich silicide of the conductive reaction layer with theelemental silicon of the substrate effective to form a conductive metalsilicide-comprising contact region over the tantalum nitride-comprisinglayer which electrically connects the conductive reaction layer with thesubstrate; the exposing, depositing and reacting being effective toreduce resistance of the tantalum nitride-comprising layer to less than1000 microohms-cm.
 47. The method of claim 46, wherein the tantalumnitride-comprising layer as-deposited is of a thickness no less than 5Angstroms.
 48. The method of claim 46, wherein the tantalumnitride-comprising layer as-deposited is of a thickness from 5 Angstromsto 10 Angstroms.
 49. The method of claim 46, wherein the exposing occursduring the depositing.
 50. The method of claim 46, wherein the exposingonly occurs during the depositing.
 51. The method of claim 46, whereinat least some of the exposing occurs prior to and separate from thedepositing.
 52. The method of claim 51, wherein all of the exposingoccurs prior to and separate from the depositing.
 53. The method ofclaim 46, wherein the conductive reaction layer has an outer portionthat at least predominately comprises the elemental metal.
 54. Themethod of claim 46, wherein the conductive reaction layer has an outerportion that at least predominately comprises the metal-rich silicide.55. The method of claim 46, wherein the reacting occurs during thedepositing.
 56. The method of claim 46, wherein the reacting occursafter the depositing.
 57. The method of claim 56, wherein the reactingdoes not occur during the depositing.
 58. The method of claim 46,wherein the exposing and the reacting occur during the depositing. 59.The method of claim 46, wherein the exposing and reacting are effectiveto reduce resistance of the tantalum nitride-comprising layer to lessthan 800 microohms-cm.
 60. The method of claim 46, wherein: the layer ofthickness no greater than 15 Angstroms is of a thickness from 5Angstroms to 10 Angstroms; the exposing occurs during the depositing;and the reacting occurs during the depositing.
 61. The method of claim46, wherein the conductive metal silicide-comprising contact region hasa thickness from 5 Angstroms to 100 Angstroms.
 62. The method of claim46, wherein the exposing, depositing and reacting are effective to formall conductive metal silicide formed over the substrate by the reactingto have no more than 10% thickness variation as determined of a thickestportion of said conductive metal silicide formed by the reacting. 63.The method of claim 46, wherein the exposing, depositing and reactingare effective to form all conductive metal silicide formed over thesubstrate by the reacting to have no more than 1% thickness variation asdetermined of a thickest portion of said conductive metal silicideformed by the reacting.
 64. The method of claim 46, wherein theexposing, depositing and reacting are effective to form all conductivemetal silicide formed over the substrate by the reacting to have from 1%to 3% thickness variation as determined of a thickest portion of saidconductive metal silicide formed by the reacting.
 65. The method ofclaim 46, wherein the conductive reaction layer is of a thickness whichis greater than that of the tantalum nitride-comprising layer.
 66. Themethod of claim 46, wherein the exposed elemental silicon-containingsurface is received within a contact opening formed within an insulativelayer.